Some years ago I woke up early because of a loud aircraft flying over. Couldn’t get back to sleep and decided to use these precious early hours to visualize the air traffic around Hilversum. Every aircraft is equipped with a device called a transponder that transmits flight data about the flight into the air. Organizations like OpenSky [https://opensky-network.org/] aggregate these data and make them available. Below a screenshot of the result.

But when revisiting this project, I felt there were more opportunities. I obtained air traffic above the Netherlands from February to April (monday's only), resulting in 11 full days of traffic. Below a first visualisation. On mobile you can also see city names when zooming in. Bright white means much traffic passes by.

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You can clearly see that Amsterdam is the hotspot of all the traffic. Let's see if there are more interesting patterns and visualisations. I won't plot the map anymore because the graphs are rendered better without.

Let's first split the traffic by altitude. If you watch this post on a computer, I recommend zooming in with ctrl+mousewheel.

Red: All the low traffic. Airfields such as Eelde, Eindhoven, Dusseldorf and Brussels are visible.
Blue: All the complex movements of traffic in and out of Amsterdam. These are standard routes being flown to keep the traffic manageable, so called STARs and SIDs.
Green: Aircraft passing over in mostly straight tracks.

There are more properties in the data, such as altitude, vertical speed and velocity. I've used different colormaps for aestetic purposes :)

Left: all the arriving flights are red and departures are blue.
Middle: This disco shows aircraft climbing or descending. The colormap is increasing with 1000m per color, starting from red for 0-1000m. Compare it with the top left graph: departing flights are quickly climbing to purple, whereas arrivals are flying lower longer. The green to yellow transitions indicate the points where arrival flights are converging for their approach.
Right: the average speed of the aircraft. Also here you see arrival routes are darker (slower) than departures.

And because COVID-19 is here, let's plot the data of the past weeks.

'Normally' there are 2700 flights above the Netherlands (including some North Sea) with a total airtime of 840 hours. That is the equivalent of about 35 aircraft flying continuously. The graph shows the dramatic slowdown to about 1/8 of the original volume.

The firelike image on the left side is slowly turning into a collection of night flies: the slowdown of traffic can be easily seen. This has been analyzed more extensively here.

I also went through callsigns that occur most often. Turns out there are some interesting patterns. Let's make it into a quiz: which pattern belongs to:

The coastguard
Aerial photography
Military flights
Emergency care flights (trauma)
Police helicopters
Commercial helicopter flights

Answers on the bottom of the post.

Let's end with some visualisations with a certain shade of blue. What type of flights do they represent?

That's it, I hope you like it!

Answers to the above:

A = Police helicopters. Interesting patterns! To the east the German police helicopter (callsign HUMMEL)
B = Aerial photography. To do their job, these flights often have dense tracks
C = Emergency medical flights. With callsign LIFELN (lifeliner), these helicopters are stationed in Amsterdam, Groningen, Rotterdam and Eindhoven.
D = Commercial helicopter flights. They mostly start from airfied Den Helder, flying personell to offshore rigs
E = Coast Guard, with callsign NCG
F = Military. In april a NATO flight departed from NATO Air Base Geilenkirchen with a Boeing E-3 Sentry

And the blues represent our flagship carrier KLM! If you want you can download the higher resolution images

Tip: Thanks to OpenSky, Datashader and some wonderful tutorials on the internet, e.g. US Census and PyViz. Used code from these examples as well.

Note: Here you can find my other posts